Geolocation of Magnetic Sources Using Vector Magnetometer Sensors

ABSTRACT

System and methods for determining an angle and/or geolocation of a dipole magnetic source relative to one or more DNV sensors. The system may include one or more DNV sensors, and a controller. The controller is configured to activate the DNV sensors, receive a set of vector measurements from the DNV sensors, and determine an angle of a magnetic source relative to the one or more DNV sensors based on the received set of vector measurements from the DNV sensors.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application claims the benefit of priority from U.S. Provisional Patent Application No. 62/360,940, filed Jul. 11, 2016, which is incorporated herein by reference in its entirety.

BACKGROUND

The present disclosure generally relates to the field of magnetometers, including for example methods and systems for geolocating magnetic sources using vector magnetometer sensors.

SUMMARY

Some embodiments relate to a system including one or more diamond nitrogen vacancy (DNV) sensors and a controller. The controller can be configured to activate the DNV sensors, receive a set of vector measurements from the DNV sensors, and determine an angle of a magnetic source relative to the one or more DNV sensors based on the received set of vector measurements from the DNV sensors. In other implementations, the controller may be configured to determine geolocation of a magnetic source relative to the one or more DNV sensors based on the received set of vector measurements from the DNV sensors.

Another embodiment relates to a geolocating device that includes one or more diamond nitrogen vacancy (DNV) sensors and means for activating the DNV sensors, receiving a set of vector measurements from the DNV sensors, and determining an angle of a magnetic source relative to the one or more DNV sensors based on the received set of vector measurements from the DNV sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one orientation of a nitrogen vacancy (NV) center in a diamond lattice.

FIG. 2 is an energy level diagram that illustrates energy levels of spin states for the NV center.

FIG. 3 is a schematic illustrating an NV center magnetic sensor system.

FIG. 4 is a graph illustrating the fluorescence as a function of applied RF frequency of an NV center along a given direction for a zero magnetic field and a non-zero magnetic field.

FIG. 5 is a graph illustrating the fluorescence as a function of applied RF frequency for four different NV center orientations for a non-zero magnetic field.

FIG. 6 is a schematic illustrating an NV center magnetic sensor system according to some embodiments.

FIG. 7 is a schematic illustrating a controller and several DNV sensors for detecting an angle and/or position of a magnetic source relative to the DNV sensors.

DETAILED DESCRIPTION

It is possible to resolve a magnetic field vector from a diamond nitrogen vacancy magnetic field sensor. In some implementations, two or more vector magnetometers may be used to resolve a position of a magnetic source. In some further implementations, a position and dipole of a magnetic source may be determined using three or more sensors. In some embodiments, magnetic sources may be geolocated using bilateration and/or vector search algorithms. Sources may be intentional or unintentional, may be passive (e.g., perturbations to Earth's geomagnetic field) or active, and may include DC, AC, or slowly varying magnetic fields. Potential applications include DNV calibration, Magnetic Anomaly Detection (MAD), industrial inventory management, magnetic beacon based applications, PNT (Position, Navigation and Timing).

NV Center, its Electronic Structure, and Optical and RF Interaction

The nitrogen vacancy (NV) center in diamond comprises a substitutional nitrogen atom in a lattice site adjacent a carbon vacancy as shown in FIG. 1. The NV center may have four orientations, each corresponding to a different crystallographic orientation of the diamond lattice.

The NV center may exist in a neutral charge state or a negative charge state. The neutral charge state uses the nomenclature NV⁰, while the negative charge state uses the nomenclature NV.

The NV center has a number of electrons including three unpaired electrons, each one from the vacancy to a respective of the three carbon atoms adjacent to the vacancy, and a pair of electrons between the nitrogen and the vacancy. The NV center, which is in the negatively charged state, also includes an extra electron.

The NV center has rotational symmetry, and as shown in FIG. 2, has a ground state, which is a spin triplet with ³A₂ symmetry with one spin state m_(s)=0, and two further spin states m_(s)=+1, and m_(s)=−1. In the absence of an external magnetic field, the m_(s)=±1 energy levels are offset from the m_(s)=0 due to spin-spin interactions, and the m_(s)=±1 energy levels are degenerate, i.e., they have the same energy. The m_(s)=0 spin state energy level is split from the m_(s)=±1 energy levels by a energy of 2.87 GHz for a zero external magnetic field.

Introducing an external magnetic field with a component along the NV axis lifts the degeneracy of the m_(s)=±1 energy levels, splitting the energy levels m_(s)=±1 by an amount 2gμ_(B)Bz, where g is the g-factor, μ_(B) is the Bohr magneton, and Bz is the component of the external magnetic field along the NV axis. This relationship is correct to a first order and inclusion of higher order corrections is a straightforward matter and should not materially affect the computational and logic steps.

The NV center electronic structure further includes an excited triplet state ³E with corresponding m_(s)=0 and m_(s)=±1 spin states. The optical transitions between the ground state ³A₂ and the excited triplet ³E are predominantly spin conserving, meaning that the optical transitions are between initial and final states which have the same spin. For a direct transition between the excited triplet ³E and the ground state ³A₂, a photon of red light is emitted with a photon energy corresponding to the energy difference between the energy levels of the transitions.

An alternate non-radiative decay route from the triplet ³E to the ground state ³A₂ via intermediate electron states exists, in which the intermediate states are thought to be intermediate singlet states A, E with intermediate energy levels. The transition rate from the m_(s)=±1 spin states of the excited triplet ³E to the intermediate energy levels is significantly greater than that from the m_(s)=0 spin state of the excited triplet ³E to the intermediate energy levels. The transition from the singlet states A, E to the ground state triplet ³A₂ predominantly decays to the m_(s)=0 spin state over the m_(s)=±1 spin states. These features of the decay from the excited triplet ³E state via the intermediate singlet states A, E to the ground state triplet ³A₂ allows that if optical excitation is provided to the system, the optical excitation will eventually pump the NV center into the m_(s)=0 spin state of the ground state ³A₂. In this way, the population of the m_(s)=0 spin state of the ground state ³A₂ may be reset to a maximum (e.g., greatest or near greatest) polarization determined by the decay rates from the triplet ³E to the intermediate singlet states.

Another feature of the decay is that the fluorescence intensity due to optically stimulating the excited triplet ³E state is less for the m_(s)=±1 states than for the m_(s)=0 spin state. This is so because the decay via the intermediate states does not result in a photon emitted in the fluorescence band, and because of the greater probability that the m_(s)=±1 states of the excited triplet ³E state will decay via the non-radiative decay path. The lower fluorescence intensity for the m_(s)=±1 states than for the m_(s)=0 spin state allows the fluorescence intensity to be used to determine the spin state. As the population of the m_(s)=±1 states increases relative to the m_(s)=0 spin, the overall fluorescence intensity will be reduced.

NV Center, or Magneto-Optical Defect Center, Magnetic Sensor System

FIG. 3 is a schematic illustrating a NV center magnetic sensor system 300 which uses fluorescence intensity to distinguish the m_(s)=±1 states, and to measure the magnetic field based on the energy difference between the m_(s)=+1 state and the m_(s)=−1 state. The system 300 includes an optical excitation source 310, which directs optical excitation to an NV diamond material 320 with NV centers. The system 300 further includes an RF excitation source 330 which provides RF radiation to the NV diamond material 320. Light from the NV diamond may be directed through an optical filter 350 to an optical detector 340.

The RF excitation source 330 may be a microwave coil, for example. The RF excitation source 330 when emitting RF radiation with a photon energy resonant with the transition energy between ground m_(s)=0 spin state and the m_(s)=+1 spin state excites a transition between those spin states. For such a resonance, the spin state cycles between ground m_(s)=0 spin state and the m_(s)=+1 spin state, reducing the population in the m_(s)=0 spin state and reducing the overall fluorescence at resonance. Similarly resonance occurs between the m_(s)=0 spin state and the ms=−1 spin state of the ground state when the photon energy of the RF radiation emitted by the RF excitation source is the difference in energies of the m_(s)=0 spin state and the ms=−1 spin state. At resonance between the m_(s)=0 spin state and the m_(s)=−1 spin state, or between the m_(s)=0 spin state and the ms=+1 spin state, there is a decrease in the fluorescence intensity.

The optical excitation source 310 may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source 310 induces fluorescence in the red, which corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 320 is directed through the optical filter 350 to filter out light in the excitation band (in the green for example), and to pass light in the red fluorescence band, which in turn is detected by the detector 340. The optical excitation light source 310, in addition to exciting fluorescence in the diamond material 320, also serves to reset the population of the m_(s)=0 spin state of the ground state ³A₂ to a maximum polarization, or other desired polarization.

For continuous wave excitation, the optical excitation source 310 continuously pumps the NV centers, and the RF excitation source 330 sweeps across a frequency range which includes the zero splitting (when the m_(s)=±1 spin states have the same energy) photon energy of 2.87 GHz. The fluorescence for an RF sweep corresponding to a diamond material 320 with NV centers aligned along a single direction is shown in FIG. 4 for different magnetic field components Bz along the NV axis, where the energy splitting between the m_(s)=−1 spin state and the m_(s)=+1 spin state increases with Bz. Thus, the component Bz may be determined. Optical excitation schemes other than continuous wave excitation are contemplated, such as excitation schemes involving pulsed optical excitation, and pulsed RF excitation. Examples, of pulsed excitation schemes include Ramsey pulse sequence, and spin echo pulse sequence.

In general, the diamond material 320 will have NV centers aligned along directions of four different orientation classes. FIG. 5 illustrates fluorescence as a function of RF frequency for the case where the diamond material 320 has NV centers aligned along directions of four different orientation classes. In this case, the component Bz along each of the different orientations may be determined. These results along with the known orientation of crystallographic planes of a diamond lattice provide not only the magnitude of the external magnetic field to be determined, but also the direction of the magnetic field.

While FIG. 3 illustrates an NV center magnetic sensor system 300 with NV diamond material 320 with a plurality of NV centers, in general the magnetic sensor system may instead employ a different magneto-optical defect center material, with a plurality of magneto-optical defect centers. The electronic spin state energies of the magneto-optical defect centers shift with magnetic field, and the optical response, such as fluorescence, for the different spin states is not the same for all of the different spin states. In this way, the magnetic field may be determined based on optical excitation, and possibly RF excitation, in a corresponding way to that described above with NV diamond material.

FIG. 6 is a schematic of an NV center magnetic sensor 600, according to some embodiments. The sensor 600 includes an optical excitation source 610, which directs optical excitation to an NV diamond material 620 with NV centers, or another magneto-optical defect center material with magneto-optical defect centers. An RF excitation source 630 provides RF radiation to the NV diamond material 620. The NV center magnetic sensor 600 may include a bias magnet 670 applying a bias magnetic field to the NV diamond material 620. Light from the NV diamond material 620 may be directed through an optical filter 650 and an electromagnetic interference (EMI) filter 660, which suppresses conducted interference, to an optical detector 640. The sensor 600 further includes a controller 680 arranged to receive a light detection signal from the optical detector 640 and to control the optical excitation source 610 and the RF excitation source 630.

The RF excitation source 630 may be a microwave coil, for example. The RF excitation source 630 is controlled to emit RF radiation with a photon energy resonant with the transition energy between the ground m_(s)=0 spin state and the m_(s)=±1 spin states as discussed above with respect to FIG. 3.

The optical excitation source 610 may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source 610 induces fluorescence in the red, which corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 620 is directed through the optical filter 650 to filter out light in the excitation band (in the green for example), and to pass light in the red fluorescence band, which in turn is detected by the optical detector 640. The EMI filter 660 is arranged between the optical filter 650 and the optical detector 640 and suppresses conducted interference. The optical excitation light source 610, in addition to exciting fluorescence in the NV diamond material 620, also serves to reset the population of the m_(s)=0 spin state of the ground state ³A₂ to a maximum polarization, or other desired polarization.

The controller 680 is arranged to receive a light detection signal from the optical detector 640 and to control the optical excitation source 610 and the RF excitation source 630. The controller may include a processor 682 and a memory 684, in order to control the operation of the optical excitation source 610 and the RF excitation source 630. The memory 684, which may include a nontransitory computer readable medium, may store instructions to allow the operation of the optical excitation source 610 and the RF excitation source 630 to be controlled.

According to some embodiments of operation, the controller 680 controls the operation such that the optical excitation source 610 continuously pumps the NV centers of the NV diamond material 620. The RF excitation source 630 is controlled to continuously sweep across a frequency range which includes the zero splitting (when the m_(s)=±1 spin states have the same energy) photon energy of 2.87 GHz. When the photon energy of the RF radiation emitted by the RF excitation source 630 is the difference in energies of the m_(s)=0 spin state and the m_(s)=−1 or m_(s)=+1 spin state, the overall fluorescence intensity is reduced at resonance, as discussed above with respect to FIG. 3. In this case, there is a decrease in the fluorescence intensity when the RF energy resonates with an energy difference of the m_(s)=0 spin state and the m_(s)=−1 or m_(s)=+1 spin states. In this way the component of the magnetic field Bz along the NV axis may be determined by the difference in energies between the m_(s)=−1 and the m_(s)=+1 spin states.

As noted above, the diamond material 620 will have NV centers aligned along directions of four different orientation classes, and the component Bz along each of the different orientations may be determined based on the difference in energy between the m_(s)=−1 and the m_(s)=+1 spin states for the respective orientation classes. In certain cases, however, it may be difficult to determine which energy splitting corresponds to which orientation class, due to overlap of the energies, etc. The bias magnet 670 provides a magnetic field, which is preferably uniform on the NV diamond material 620, to separate the energies for the different orientation classes, so that they may be more easily identified.

Systems and Methods for Angle Determination and/or Geolocating Magnetic Sources

The NV center magnetic sensor is capable of resolving a vector of a magnetic source. High sensitivity, high bandwidth, full vector magnetometry sensing may be provided by a set of DNV sensors to estimate the location of a fixed magnetic source with known dipole orientation, the location and dipole orientation of a fixed magnetic source with unknown dipole orientation, the location of an AC magnetic source with fixed dipole orientation, and/or the location of a rotating dipole magnetic source with known plane of rotation relative to sensors. Alternatively to the dipole orientation being known, the dipole moment and position may be deteremined using the sensing.

To determine the geolocation of the magnetic source, a controller receives the vector measurement inputs from two or more of the magnetometers and computes a score function and associated gradient for candidate magnetic source locations and orientations based on the magnetic fields as measured at a set of spatially distributed (DNV) vector magnetometer sensors. In some implementations, the controller can be applied to locate DC or AC magnetic sources. The system utilizes the vector difference between sensors as a means of mitigating common-mode spatially flat interfering sources and/or the full vector estimates from each sensor to provide more degrees of freedom to estimate the source location and orientation.

In some systems, an array of magnetometers measuring only scalar values utilizes Anderson functions to perform certain Magnetic Anomaly Detection (MAD) tasks. Anderson functions describe how a magnetic field amplitude and gradient of the full field amplitude vary as a function of relative geometry with respect to a magnetic source or disturbance. In such Anderson scalar systems, the array of scalar measurements may be compared to expected Anderson function values for a guessed location of magnetic source through trial and error. Such systems require a large array of sensors covering a large area and multiple iterative guesses to determine the location of the magnetic source. In other systems, a geolocation magnetic sensor may use a three-dimensional magnetic sensor and a multi-axis gradiometer with direct inversion of a 1st order expansion formula to provide a closed form solution for location of an RFID tag. Such a sensor consists of three orthogonal loop coils, three orthogonal planar gradiometers and three orthogonal axial gradiometers, thus requiring a large and complex sensor apparatus with limited sensitivity. Moreover, for the orthogonal loops of wire, the magnetic field detection is limited to AC fields for inducing current within the looped coils.

In contrast, the solution presented herein can minimize the number of magnetometers needed and reduce the spatial area needed to perform magnetic source geolocation. In particular, the instantaneous vector DNV sensors provide high bandwidth and can utilize dipole field matching to geolocate a magnetic source. Such DNV sensors provide a higher sensitivity and can provide vector estimation in a single compact sensor. In some implementations, improvements in the DNV sensitivity and 1/f noise compensation allow extension of geolocation to DC, slowly varying AC, and higher frequency AC tones. Low frequency AC sources offer particular potential benefits in salt-water environments where suppression of magnetic fields increases with frequency. In some embodiments described herein, the geolocation with full vector magnetometers offers improved capability over scalar full-field magnetometers and/or associated full field sensors and gradiometers. Potential incorporation of multiple vector DNV sensors permits full three by three Jacobian (gradient matrix) computation from 4 compact sensors.

Referring to the system of FIG. 7, four DNV sensors 720, such as those described above in reference to FIGS. 1-6, are shown coupled to a controller 710 and positioned relative to a magnetic source. The controller 710, in addition to controlling the DNV sensors 720 and receiving data from the sensors 720, may perform data processing on the data. In this regard, the controller 710 may include a subcontroller to control and receive data from the sensors 720, and one or more further subcontroller to perform data processing on the data. Each of the DNV sensors 720 takes multiple measurements over time and/or can take a single measurement during the same time window. In some implementations, the controller 710 may have the set of DNV sensors 720 take an initial measurement with no magnetic source 730 present to provide a base measurement such that a variation in the measurement from the DNV sensors 720 can be detected when a magnetic source 730 is present. That is, the controller 710 may store a base magnetic field measurement to compare to subsequent measurements from the DNV sensors 720. Subsequent measurements can be compared to the base measurement to detect the presence of a magnetic source 730. In some implementations, the earth's magnetic field and/or the background magnetic field can change over time. Thus, in some instances, if there are relatively minor differences between the base measurement and the subsequent measurement, this may be due to changes in the earth's magnetic field. Accordingly, in some implementations, it may be determined that the magnetic source 730 is present if the differences between the base measurement and the subsequent measurement is larger than a threshold amount. The threshold amount can be large enough that changes from the base measurement to the subsequent measurement caused by the changes in the earth's magnetic field are ignored, but small enough that changes caused by the presence or movement of a magnetic source are larger than the threshold amount. Using the subsequent measurement, a plane angle and/or a geolocation for the magnetic source 730 can be determined.

In some implementations, the DNV sensors 720 each take a measurement of a magnetic field once per second. The controller 710 can receive vector magnetic measurements taken by the DNV sensors 720. In some implementations, the measurements are received simultaneously from the DNV sensors 720. The controller 710 receives each of the measurements and stores them as sets of measurements. The most recently received set of measurements can be compared to the previously received set of measurements. As a magnetic source 730 moves closer or moves around when in detection range, the magnetic source disrupts the magnetic field detected by the DNV sensors 720. The DNV sensors 720 may be distributed in any geometric configuration and the magnetic field at the points detected by the DNV sensors 720 may be affected differently based on the location of the magnetic source 730.

In an illustrative embodiment, the plane angle, size, and/or location of a rotating magnetic source can be determined based on the measurements from the DNV sensors. For plane angle estimation relative to the DNV sensors:

M=A ^(T) R _(r2D) B+W

where W˜(NCO, I), R_(r2D) is the transform of the positional coordinates of a room or area to the diamond, and B is the detected magnetic field. For a rotating magnetic source in the same plane as a DNV sensor and with a rotation axis along the z-axis of the area and a moment in the X-Y plane of the area with a plane angle of θ, then the magnetic field, B, can be defined as:

$B = {R_{\theta}\begin{bmatrix} {2\; {\cos \left( {{\omega \; t} + \phi} \right)}} \\ {\sin \left( {{\omega \; t} + \phi} \right)} \\ 0 \end{bmatrix}}$

where φ is an unknown phase offset and t=[t₁, t₂, . . . , t_(n)] is the time vector. Thus,

$M = {{A^{T}R_{r\; 2D}{R_{\theta}\begin{bmatrix} {2\; {\cos \left( {{\omega \; t} + \phi} \right)}} \\ {\sin \left( {{\omega \; t} + \phi} \right)} \\ 0 \end{bmatrix}}} + W}$

Converting the cosine and sine terms using Euler's formula,

$M = {{A^{T}R_{r\; 2D}{R_{\theta}\begin{bmatrix} {{e^{i\; \phi}e^{i\; \omega \; t}} + {e^{{- i}\; \phi}e^{{- i}\; \omega \; t}}} \\ {{\frac{1}{2}e^{i\; \phi}e^{i\; \omega \; t}} - {\frac{1}{2}e^{{- i}\; \phi}e^{{- i}\; \omega \; t}}} \\ 0 \end{bmatrix}}} + W}$

which be further reduced to

M=A ^(T) R _(r2D) R _(θ) E+W

Given a known M, R_(r2D), and A values, then {circumflex over (θ)} can be determined since ¾AA^(T)=I. Accordingly,

${\frac{3}{4}R_{\theta}^{T}R_{r\; 2D}^{T}{AM}} = {E + W^{\prime}}$

To determine the {circumflex over (θ)} according to a first implementation, the controller can perform matched filtering against the e^(iωt) term to determine the R_(θ) transform that maximizes the x-component. Thus, the controller can calculate:

$R_{\hat{\theta}} = {\begin{matrix} {\arg \; \max} \\ R_{\theta} \end{matrix}{{\frac{3}{4}R_{\theta}^{T}R_{r\; 2D}^{T}{{AM}\left( e^{i\; \omega \; t} \right)}^{H}}}}$

where (e^(iωt))^(H) is the conjugate transpose and R_(θ) ^(T)R_(r2D)AM(e^(iωt))^(H) is a three by one vector that can be obtained directly from Fast Fourier Transform.

In some implementations, the amplitude ratio between a dominant direction and a perpendicular direction of the dipole can be leveraged and the ninety degree phase offset can also be used. That is,

$R_{\hat{\theta}} = {\begin{matrix} {\arg \; \max} \\ R_{\theta} \end{matrix}{{\left\lbrack {2 - {i\; 0}} \right\rbrack \frac{3}{4}R_{r\; 2D}^{T}R_{\theta}^{T}{{AM}\left( e^{i\; \omega \; t} \right)}^{H}}}}$

In yet a further implementation, an Orthogonal Procrustes algorithm can be used by the controller to determine the R_(θ) that minimizes

${{{R_{\theta}E} - {\frac{3}{4}R_{r\; 2D}^{T}{AM}}}}_{F}$

In further implementations, the DNV sensors 720 and the controller 710 can be used for geolocation through dipole field matching. That is, the vector measurements of the DNV sensors 720 of the magnetic source 730 can be compared to a set of known orientations and/or configurations for a dipole magnetic source. In some implementations, a time series of vector measurements can be compared to a time series of known orientations and/or configurations for a dipole magnetic source. The controller 720, via a sub-controller for example, can compare the vector measurements to the set of known orientations and/or configurations for a dipole magnetic source to determine the maximum (e.g., greatest or near greatest). The maximum orientation and/or configuration is then set as the geolocation and/or orientation of the magnetic source 730 relative to the DNV sensors 720. By comparing the vector measurements to known orientations and/or configurations of magnetic sources, a direct determination of the angle of the dipole magnetic source and/or location can be determined.

In an example implementation, five DNV sensors 720 may be used with the controller 710 to determine a geolocation of a magnetic source and associated moment vector from the resulting vector magnetic field measured by the five DNV sensors 720. Other numbers of DNV sensors 720 may also be used, such as two or three. The controller 710 is electrically coupled to the five DNV sensors 720 to receive data from the DNV sensors. In some implementations, the controller 710, which may include one or more subcontrollers, may be in data communication with a DNV sensor controller to receive vector data from the DNV sensor controller. In other implementations, the controller 710 may be in direct data communication with the DNV sensors 720 to receive raw data output. The controller 710 can include an initial position vector for the DNV sensors 720, such as [X_coord, Y_coord, Z_coord] defining each DNV sensor location.

The example implementation may also generate a Monte Carlo set of dipole data based on an approximation of a single magnetic source. The controller 710 can include an upper bound and lower bound vector defining an upper position and lower position boundary for the Monte Carlo set of dipole data for the approximated single magnetic source relative to the DNV sensors 720. In some implementations, the controller 710 may also store an initial start position for generating the Monte Carlo set of dipole data for the approximated single magnetic source. The initial start position may be randomly generated positional X, Y, and Z coordinates and/or may be static X, Y, and Z values. The approximated single magnetic source may include a static dipole moment.

To generate the Monte Carlo set, the controller 710 is configured to define three by one vectors for each magnetic field and corresponding gradients that would be detected by each DNV sensor for the approximated single magnetic source, such as [SensorField#, SensorFieldGradientX, SensorFieldGradientY, SensorFieldGradientZ], which is determined as a function of the sensor position, a position of the approximated single magnetic source, and the dipole moment. A Monte Carlo method can be performed for a given root mean square (RMS) noise per vector component. A geolocation function generates data for the approximated single magnetic source and estimated dipole moment based on the sensor positions, the measured resultant magnetic field at each sensor with Monte Carlo generated RMS noise per vector component, the upper and lower bounds, and the initial start position. The geolocation function also generates data for a measured magnetic source based on the measured magnetic vectors of the DNV sensors 720, the sensor positions, the dipole moment, an initial dipole position estimate, and an upper bound and a lower bound for the dipole position. That is, the geolocation function may utilize the magnetic field data from the DNV sensors to determine a position and dipole moment of the magnetic source based on dipole field matching.

In some implementations, the initial dipole position estimate and dipole moment vector estimate may be modified based on a scoring function based on an error fit between the estimated position and moment of the magnetic source and the measured dipole magnetic fields by the DNV sensors. In some implementations, a least squares algorithm may be used to perform a constrained least squares fit to optimize performance. Below is provided exemplary computer code (MATLAB

% ========================================================================= % Script to evaluate magnetic field from a dipole at five sensors. % ========================================================================= %% Initialization clear; %% Define grid points % X = Right on monitor, Y = Up on monitor, Z = Out of monitor towards user. %% Define Sensor Locations: sensor1Location = [−10 0 1]′; % (3 x 1) (m) sensor2Location = [0 0 1]′; % (3 x 1) (m) sensor3Location = [10 0 1]′; % (3 x 1) (m) sensor4Location = [−5 5 1.5]′; % (3 x 1) (m) sensor5Location = [5 5 1.5]′; % (3 x 1) (m) sensorPos = [sensor1Location, sensor2Location, sensor3Location, ... sensor4Location, sensor5Location]; %% Define initial estimates and bounds for search algorithm: % Define initial dipole position and moment estimates as well as associated % upper and lower search bounds for the position and moment estimates MC_initPosMoment = [0, 20, 1, 10, 10, 10]; MC_posMomentLowerBound = [−80, −15, 0, −100, −100, −100]; MC_posMomentUpperBound = [ 80, 100, 2, 100, 100, 100]; %% Define Test Dipole Moment and Position: % % Define Magnet Test Location for analysis testDipolePosition = [9, 15, 1.25 ] % % Define Magnet Dipole magnitude and orientation for analysis dipoleMoment = 63.8 * unit([1 1 1]) % (3 x 1) (T) %% Specify RMS noise (per magnetic field component) noise_nT = 0.1 % Gaussian b field error (nT) per xyz component %% Generate truth data for all sensor locations [ sensorField, ... sensorFieldGradX, sensorFieldGradY, sensorFieldGradZ ] =... dipoleBField_wDipolePosGradient_SingleDipole(... sensorPos, testDipolePosition′, dipoleMoment′);% [ sensor1Field, ... measuredB = 1e9*sensorField; measuredBfield_mag_nT = sqrt(sum(measuredB. {circumflex over ( )}2,1)) %% Run Monte Carlo for given RMS noise per vector component nMonteCarloTrials = 40; for ii = 1:nMonteCarloTrials, MCmeasB = measuredB + noise_nT*randn(size(measuredB)); % Call Geolocation solver: [ magnet3dPosMoment (ii,:) ] = xyzGeolocateBfield_wDipole_multiBfit( ...  MCmeasB, ...  sensorPos, ...  MC_initPosMoment, MC_posMomentLowerBound, MC_posMomentUpperBound); end %% Compute sample Monte Carlo statistics on the accuracy of the target % dipole position and moment estimates: meanMCdipolePos = mean(magnet3dPosMoment(:,1:3),1) meanMCdipoleMoment = mean(magnet3dPosMoment(:,4:6),1) MCdipolePosErr = magnet3dPosMoment(:,1:3)−... repmat(testDipolePosition,nMonteCarloTrials,1); MCdipoleMomentErr = magnet3dPosMoment(:,4:6)−... repmat(dipoleMoment,nMonteCarloTrials,1); meanMCdipolePosErr = mean(MCdipolePosErr,1) meanMCdipoleMomentErr = mean(MCdipoleMomentErr,1) stdMCdipolePosErr = std(MCdipolePosErr,1) stdMCdipoleMomentErr = std(MCdipoleMomentErr,1) rmsMCdipolePosErr = rms(MCdipolePosErr,1) rmsMCdipoleMomentErr = rms(MCdipoleMomentErr,1) %% End of Monte Carlo Geolocation Script % ========================================================================= % Function to estimate magnetic dipole position and moment vector from % measurements of the resulting magnetic field at multiple sensors. % ========================================================================= function [ magnet3dPosMoment ] = xyzGeolocateBfield_wDipole_multiBfit( ... measBvec, ... sensorPos, ... dipolePosXYZMomentXYZ_init, ... dipolePosXYZMomentXYZ_LB, dipolePosXYZMomentXYZ_UB) % xyzGeolocateBfield_wDipole_multiBfit.m % Function estimates the geolocation and moment of a magnetic dipole % target from measured estimates of the magnetic field caused by the % dipole source at a set of known sensor positions (and orientations). % Define geolocation score function to be optimized: geoScoreFunWrapper = @(dipolePosXYZMomentXYZ) geoDipoleErrorFun6stateFitXYZDipole( ... dipolePosXYZMomentXYZ(1:3), ... measBvec, ... sensorPos, dipolePosXYZMomentXYZ(4:6)′ ); % If upper and lower bounds are not provided in the function, the following % commands provide representative bounds for an envisioned scenario. if (nargin < 5) dipolePosXYZMomentXYZ_UB = [ 2,3,2, 100, 100, 100]; end if (nargin < 4) dipolePosXYZMomentXYZ_LB = [−2,1,0, −100, −100, −100]; end % If an initial position and dipole moment estimate is not provided, the % following commands provide a representative initial estimate for an % envisioned scenario. if (nargin < 3) dipolePosXYZMomentXYZ_init = [0,2,1, 1, 1, 1]; end % Perform optimization using built-in lsqnonlin algorithm to perform % constrained ordinary least squares % Set options for contrained nonlinear least square solver: options = optimoptions (‘lsqnonlin’, ... ‘TolX’, 1e−16, ‘TolFun’, 1e−16, ... ‘MaxFunEvals’, 4000, ‘MaxIter’, 1000, ‘Display’, ‘off’, ... ‘Jacobian’,‘on’); % Call nonlinear least squares solver: [magnet3dPosMoment, ~] = lsqnonlin( geoScoreFunWrapper, ... dipolePosXYZMomentXYZ_init, ... dipolePosXYZMomentXYZ_LB, dipolePosXYZMomentXYZ_UB, options); end % ========================================================================= % Function to compute the error between a set of measured magnetic field % vectors at known sensor locations and the expected magnetic field at the % same locations for a candidate dipole moment and position. % ========================================================================= function [multiBerror, multiBJacobian] = ... geoDipoleErrorFun6stateFitXYZDipole( dipolePosXYZ, ... measBvec, sensorPos, dipoleMoment )  % Function call computes the error between a set of measured magnetic  % field vectors, “measBvec” and the expected magnetic fields for a scenario  % described by sensors at position “sensorPos” and magnetic dipole sources  % with moments “dipoleMoment” located at positions “dipolePosXYZ”.  % The function call further calculates the Jacobian matrix associated with  % the given error function.  % Compute the resulting magnetic field at a given sensor Position for a  % dipole at given position with given dipole moment  [ sensorField, ...   sensorFieldGradX, sensorFieldGradY, sensorFieldGradZ, ...   sensorFieldGrad_mX, sensorFieldGrad_mY, sensorFieldGrad_mZ ] = ...   dipoleBField_wDipolePosVecGradient_SingleDipole(...   sensorPos, dipolePosXYZ′, dipoleMoment);  % Compute the error function between the measured and expected magnetic  % fields at the given sensor locations due to the specified candidate set  % of dipole positions and moments.  multiBerror = [measBvec − 1e9*sensorField];  % Calculate Jacobian matrix:  if nargout > 1  Jacobian = zeros(1,length(dipolePosXYZ));  multiBJacobian = −1e9*[ ... sensorFieldGradX(:), sensorFieldGradY(:), sensorFieldGradZ(:), ... sensorFieldGrad_mX(:), sensorFieldGrad_mY(:), sensorFieldGrad_mZ(:) ];  end end % ========================================================================= % Function to compute the magnetic field and corresponding gradient vectors % at specified sensor positions based upon a magnetic dipole with specified % moment and position. % % USAGE % [bField, bFieldGradX, bFieldGradY, bFieldGradZ] = ... % dipoleBField_wDipolePosGradient(sPos,dPos,m,mu) % INPUTS % sPos - the sensor position (3x1 or 3xN column) vector % dPos - the dipole position (3x1) vector % m - the (3x1) vector magnetic moment (n*I*A, right-hand rule direction) % Note: size(dPos) = size(m) % mu - the scalar permeability (default to mu0) % OUTPUTS % bField - the (3XN matrix) Bfield vectors % bFieldGradX - the (3XN matrix) gradient vectors of Bfield w.r.t. X % bFieldGradY - the (3XN matrix) gradient vectors of Bfield w.r.t. Y % bFieldGradZ - the (3XN matrix) gradient vectors of Bfield w.r.t. Z % ========================================================================= function [bField,bFieldGradX,bFieldGradY,bFieldGradZ] = ... dipoleBField_wDipolePosGradient_SingleDipole(sPos,dPos,m,mu) if nargin < 4  mu = util.Physics.MAGNETIC_CONSTANT; end if (size(dPos) ~= size(m))  error (‘# dipole Positions must match # dipole orientations’) end % Make r and m have equal size if size(sPos,2) < size (m,2) % Impossible for single Dipole function  sPos = repmat(sPos, 1, size(m,2)); elseif size(m,2) < size(sPos,2)  m = repmat(m, 1, size(sPos, 2));  dPos = repmat(dPos, 1, size(sPos, 2)); end r = sPos − dPos; assert (size(r,2) == size(m,2), ...  ‘Input r and m must have size in 2nd dim equal to each other or to 1’); %% Compute b field rMag = sqrt(sum(r.*r)); rMag5 = rMag.{circumflex over ( )}5; rMag7 = rMag.{circumflex over ( )}7; mDotR = sum(m .* r); % 1XN row-vector of magnetic moment dotted with % N radial vectors bField = mu/(4*pi)*... ( 3*r.*repmat(mDotR./rMag5,3,1) − m.*repmat(rMag,3,1).{circumflex over ( )}(−3) ); %% Compute b field gradient with respect to coordinates X, Y, and Z bFieldGradX = −3*mu/(4*pi)*( ...  r.*(repmat(−5*r(1,:).*mDotR./rMag7 + m (1,:)./rMag5 , 3, 1)) − ...  − m.*repmat( r(1,:)./rMag5 , 3, 1) + ...  [mDotR./rMag5; zeros(size(mDotR)); zeros(size(mDotR))] ); bFieldGradY = −3*mu/(4*pi)*( ...  r.*(repmat(−5*r(2,:).*mDotR./rMag7 + m(2,:)./rMag5 , 3, 1)) − ...  − m.*repmat( r(2,:)./rMag5 , 3, 1) + ...  [zeros(size(mDotR)); mDotR./rMag5; zeros(size(mDotR))] ); bFieldGradZ = −3*mu/(4*pi)*( ...  r.*(repmat(−5*r (3,:).*mDotR./rMag7 + m(3,:)./rMag5 , 3, 1)) − ...  − m.*repmat( r(3,:)./rMag5 , 3, 1) + ...  [zeros(size(mDotR)); zeros(size(mDotR)); mDotR./rMag5] ); end

The description is provided to enable any person skilled in the art to practice the various embodiments described herein. While various figures and embodiments are referenced, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the claims.

There may be many other ways to implement the claimed technology. Various functions and elements described herein may be partitioned differently from those shown without departing from the scope of the subject technology. Various modifications to these embodiments may be readily apparent to those skilled in the art, and generic principles defined herein may be applied to other embodiments. Thus, many changes and modifications may be made to the subject technology, by one having ordinary skill in the art, without departing from the scope of the subject technology.

Phrases such as an aspect, the aspect, another aspect, some aspects, one or more aspects, an implementation, the implementation, another implementation, some implementations, one or more implementations, an embodiment, the embodiment, another embodiment, some embodiments, one or more embodiments, a configuration, the configuration, another configuration, some configurations, one or more configurations, the subject technology, the disclosure, the present disclosure, other variations thereof and alike are for convenience and do not imply that a disclosure relating to such phrase(s) is essential to the subject technology or that such disclosure applies to all configurations of the subject technology. A disclosure relating to such phrase(s) may apply to all configurations, or one or more configurations. A disclosure relating to such phrase(s) may provide one or more examples. A phrase such as an aspect or some aspects may refer to one or more aspects and vice versa, and this applies similarly to other foregoing phrases

A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” The term “some” refers to one or more. Headings and subheadings are used for convenience only, do not limit the subject technology, and are not referred to in connection with the interpretation of the description of the subject technology. All structural and functional equivalents to the elements of the various embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the subject technology. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description.

Implementations of the subject matter and the operations described in this specification can be implemented in digital electronic circuitry, or in computer software embodied on a tangible medium, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. The subject matter described in this specification can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions, encoded on one or more computer storage media for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, the program instructions can be encoded on an artificially-generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. A computer storage medium can be, or be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially-generated propagated signal. The computer storage medium can also be, or be included in, one or more separate components or media (e.g., multiple CDs, disks, or other storage devices). Accordingly, the computer storage medium is both tangible and non-transitory.

The operations described in this specification can be performed by a data processing apparatus on data stored on one or more computer-readable storage devices or received from other sources.

The terms “data processing apparatus,” “computing device,” or “processing circuit” encompass all kinds of apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, a system on a chip, or multiple ones, a portion of a programmed processor, or combinations of the foregoing. The apparatus can include special purpose logic circuitry, e.g., an FPGA or an ASIC. The apparatus can also include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, a cross-platform runtime environment, a virtual machine, or a combination of one or more of them. The apparatus and execution environment can realize various different computing model infrastructures, such as web services, distributed computing and grid computing infrastructures.

A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, object, or other unit suitable for use in a computing environment. A computer program may, but need not, correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub-programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for performing actions in accordance with instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, e.g., a mobile telephone, a personal digital assistant (PDA), a mobile audio or video player, a game console, a Global Positioning System (GPS) receiver, or a portable storage device (e.g., a universal serial bus (USB) flash drive), to name just a few. Devices suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

To provide for interaction with a user, implementations of the subject matter described in this specification can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input.

While this specification contains many specific implementation details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular implementations. Certain features described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated in a single software product or packaged into multiple software products embodied on tangible media.

References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms.

Thus, particular implementations of the subject matter have been described. Other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain implementations, multitasking and parallel processing may be advantageous.

The claims should not be read as limited to the described order or elements unless stated to that effect. It should be understood that various changes in form and detail may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims. All implementations that come within the spirit and scope of the following claims and equivalents thereto are claimed. 

1. A system comprising: one or more diamond nitrogen vacancy (DNV) sensors; and a controller configured to: activate the DNV sensors, receive a set of vector measurements from the DNV sensors, and determine an angle of a magnetic source relative to the one or more DNV sensors based on the received set of vector measurements from the DNV sensors.
 2. (canceled)
 3. The system of claim 1, wherein the magnetic source is a rotating magnetic source.
 4. The system of claim 1, wherein the controller is further configured to determine the position and dipole moment of the magnetic source based on the received set of vector measurements from the DNV sensors.
 5. The system of claim 4, wherein the angle of the magnetic source relative to the one or more DNV sensors is determined based in part on the determined position and dipole moment of the magnetic source.
 6. The system of claim 1, wherein the number of DNV sensors is three or more.
 7. A system comprising: one or more diamond nitrogen vacancy (DNV) sensors; and a controller configured to: activate the DNV sensors, receive a set of vector measurements from the DNV sensors, and determine geolocation of a magnetic source relative to the one or more DNV sensors based on the received set of vector measurements from the DNV sensors.
 8. (canceled)
 9. The system of claim 7, wherein the controller is further configured to determine the position and dipole moment of the magnetic source based on the received set of vector measurements from the DNV sensors.
 10. The system of claim 9, wherein the geolocation of the magnetic source relative to the one or more DNV sensors is determined based in part on the determined position and dipole moment of the magnetic source.
 11. The system of claim 7, wherein the number of DNV sensors is three or more.
 12. A geolocating device comprising: one or more diamond nitrogen vacancy (DNV) sensors; and a means for activating the DNV sensors, receiving a set of vector measurements from the DNV sensors, and determining an angle of a magnetic source relative to the one or more DNV sensors based on the received set of vector measurements from the DNV sensors.
 13. (canceled)
 14. The device of claim 12, wherein the magnetic source is a rotating magnetic source.
 15. The device of claim 12, further including a means for determining the position and dipole moment of the magnetic source based on the received set of vector measurements from the DNV sensors.
 16. The device of claim 12, wherein the number of DNV sensors is three or more.
 17. A system comprising: one or more diamond nitrogen vacancy (DNV) sensors; and a controller configured to: activate the DNV sensors, receive a set of vector measurements from the DNV sensors, and determine the position and dipole moment of the magnetic source based on the received set of vector measurements from the DNV sensors.
 18. (canceled)
 19. A geolocating device comprising: one or more diamond nitrogen vacancy (DNV) sensors; and a means for activating the DNV sensors, receiving a set of vector measurements from the DNV sensors, and determining the position and dipole moment of a magnetic source relative to the one or more DNV sensors based on the received set of vector measurements from the DNV sensors.
 20. (canceled)
 21. A system comprising: one or more magneto-optical defect center sensors; and a controller configured to: activate the magneto-optical defect center sensors, receive a set of vector measurements from the magneto-optical defect center sensors, and determine geolocation of a magnetic source relative to the one or more magneto-optical defect center sensors based on the received set of vector measurements from the magneto-optical defect center sensors.
 22. A geolocating device comprising: one or more magneto-optical defect center sensors; and a means for activating the magneto-optical defect center sensors, receiving a set of vector measurements from the magneto-optical defect center sensors, and determining the position and dipole moment of a magnetic source relative to the one or more magneto-optical defect center sensors based on the received set of vector measurements from the magneto-optical defect center sensors.
 23. A geolocating device comprising: one or more magneto-optical defect center sensors; and a means for activating the magneto-optical defect center sensors, receiving a set of vector measurements from the magneto-optical defect center sensors, and determining an angle of a magnetic source relative to the one or more magneto-optical defect center sensors based on the received set of vector measurements from the magneto-optical defect center sensors. 